1. Field of the Invention
This invention relates generally to mechanically stabilized embankment systems, and more particularly to a method for constructing a mechanically stabilized earthen embankment using semi-extensible steel soil reinforcements.
2. Description of Related Art
The prior art teaches various forms of mechanically stabilized embankment systems for stabilizing earthen embankments. These systems include a wall facing element connected to elongate soil reinforcement elements that extend into the earthen embankment. The prior art elongate soil reinforcement elements fall into three categories: (1) extensible reinforcements made of plastic or other material that stretch under pressure, (2) non-extensible rods made of steel or the like that have a deformable region in a proximal portion of the rod adjacent the wall facing element, to accommodate some relative movement between the rods and the wall facing element (e.g., in the event of an earthquake), and (3) non-extensible rods that are bent in various manners for the purpose of anchoring the rod in the earthen embankment.
In the first category, extensible plastic reinforcements are effective in accommodating movement of the earthen embankment along the entire length of the plastic reinforcements. The disadvantage of such systems is that the reinforcements are completely extensible, and there is nothing to limit the stretching of the reinforcements. Stretching the reinforcements weakens them and may cause movement of the face and failure of the system.
In the second category, non-extensible steel rods with deformable sections adjacent the wall facing element are useful in mitigating damage from earthquakes and some movement of the rods immediately adjacent the wall facing element, while still maintain support for the wall facing. Munster, U.S. Pat. No. 1,762,343, for example, teaches a system wherein the anchor elements are slidably attached to the retaining wall. Hilfiker, U.S. Pat. No. 4,343,572, teaches a system wherein the anchor elements include deformable sections adjacent the wall facing, so that the anchor element may move with the embankment in the event of an earthquake or other form of movement adjacent the wall facing. While the steel rods of this second category function to deform under the stresses adjacent the wall, they are not able to accommodate stresses placed upon the rods inside the earthen embankment. Since the rods are not extensible within the earthen embankment, they must be made with sufficiently steel to prevent failure within the earthen embankment, this driving up the costs of the system.
There are several prior art references that teach steel rods, straps, and the like, that include bent portions to provide limited extensibility. Most pertinent of these references, Brown, U.S. Pat. No. 7,270,502, teaches steel reinforcing straps (or rods) that are corrugated, having bent sections along the entire length of the straps. The corrugated structure of the straps is intended to provide pull out resistance, and also semi-extensibility; however, it is difficult to limit the extensibility of the straps, since the entire length of the strap is subject to being pulled straight. Sufficient force exerted on the straps tends to cause too much extension, which can lead to failure of the wall facing. Furthermore, as the bent segments are straightened under the stress, the straps lose pull out resistance, further compounding the problem.
Other references teach steel reinforcement rods having a bent “swiggle” anchor at the distal portion opposite the wall. The “swiggle” anchor functions to anchor the rods more firmly in the earthen embankment. An example of such a construction is shown in Hilfiker, U.S. Pat. No. 4,834,584. However, this form of “swiggle” anchor is unable to accommodate movement within the earthen structure.
Other prior art patents of interest include Hilfiker, U.S. Pat. No. 7,073,983, Hilfiker, U.S. Pat. No. 4,929,125, Hilfiker, U.S. Pat. No. 4,993,879. All of the above-described references are hereby incorporated by reference in full.
The prior art teaches extensible plastic reinforcements. The prior art also teaches the use of non-extensible steel rods that include deformable, bent portions, at either the proximal or distal portions, or along the entire length of the rods. However, the prior art does not teach elongate soil reinforcement elements that only include having bent sections at the location of maximum force. Such “semi-extensible” elements enable limited movement within the earthen embankment adjacent the location of maximum force, as described below, without weakening the elongate soil reinforcement elements and without providing too much extension that could lead to the failure of the wall facing. The present invention fulfills these needs and provides further related advantages as described in the following summary.